This invention relates generally to the replacement of in-bed boiler tubes for fluidized bed boilers and in particular to modular in-bed steam tube units for fluidized bed boilers.
Fluidized bed construction (FBC) is a practical, efficient way to burn coal and other fuels in an environmentally acceptable manner. In addition, fluidized bed boilers are able to utilize a wide variety of coals including high sulfur and high-ash coals and still obtain optimum results. As much as 98% of the sulfur in the coal can be absorbed and changed to a dry calcium sulfate, which is not harmful to the environment. As a result, FBC technology, which has been known for many years, has recently become a growing force in many commercial operations.
A coal-fired fluidized bed boiler burns particles of coal in a bed of limestone that is suspended in air that is forced upwards from the bottom and causes the limestone particles to percolate upwards like a liquid through the bed. As the velocity of air is increased, the limestone becomes suspended and the bed resembles a boiling fluid.
Steam boiler tubes immersed in the bubbling bed of fuel and limestone deteriorate rapidly. Tube replacement requires extensive downtime in order to cut out the deteriorated tubes, generally by burning out the tubes and installing new tubes by welding. This is a laborious and time-consuming process which includes extending the down-time of the boiler unit undergoing repairs.
Patents relating to tube bundles extending into a heated chamber and housing connections to a manifold or heater outside the chamber are as follows:
______________________________________ Inventor U.S. Pat. No. Granted ______________________________________ Johanson 1,820,979 Sept. 1, 1931 Epstein et al. 1,873,638 Aug. 23, 1932 Mahoney 1,918,608 July 18, 1933 Lavender 2,006,836 July 2, 1935 Van Seggern 2,016,759 Oct. 8, 1935 Hofmeister 2,660,410 Nov. 24, 1953 Pellmyr 2,938,712 May 31, 1960 Nevins 3,244,225 Apr. 5, 1966 Henderson 3,554,706 Jan. 12, 1971 ______________________________________
A patent relating to a fluidized bed boiler is U.S. Pat. No. 4,240,377 issued to Johnson Dec. 23, 1980. A review of these patents has not disclosed the features of the embodiments of the disclosure discussed hereinbelow in the opinion of the applicant. For this reason, no detailed discussion of these patents is set forth here.